1. Field of the Invention
The invention relates to fiber optic gyroscopes (FOGs) and in particular to integration techniques that utilize only a single light source to implement a multi-axis FOG transceiver in a small, compact form factor.
2. Description of the Related Art
A FOG is a device that uses the propagation of light beams in an optical fiber coil to detect mechanical rotation of the fiber coil. The sensor is a coil of as much as 5 km of optical fiber. The typical implementation provides that two light beams be launched into the fiber in opposite directions. Due to an optical phenomenon known as the Sagnac effect, the beam traveling against the rotation experiences a slightly shorter path than the other beam, resulting in a relative phase shift. The amount of the phase shift of the original two beams can be measured by determining how the beams interfere with each other when they are combined. The intensity of the combined beam then depends on the rotation rate of the fiber coil about its axis.
A FOG provides extremely precise rotational rate information, in view of its lack of cross-axis sensitivity to vibration, acceleration, and shock. Unlike the classic spinning-mass gyroscope, the FOG has virtually no moving parts and no inertial resistance to movement. The FOG also provides a higher resolution than a ring laser gyroscope and is utilized in internal navigation systems requiring a high degree of accuracy.
There are two types of FOG systems, closed loop and open loop. In a closed loop system, a feedback path is defined so as to maintain the phase difference between the light beams constant after the beams exit the ends of the fiber coil. The amount of feedback needed to maintain the fixed phase relation is therefore indicative of the rate of rotation of the coil about its axis.
Open loop FOG systems calculate the rotation rate by way of amplitude measurements taken along an interference curve which results when the two exiting light beams are recombined.